Surface sensibility and stability of AlGaN/GaN ion-sensitive field-effect transistors with high Al-content AlGaN barrier layer

Abstract As pH sensors, AlGaN/GaN ion-sensitive field-effect transistors (ISFETs) with stacked and high Al-content AlGaN barrier have been fabricated to evaluate the sensing ability and surface reliability. It demonstrates that the stacked barrier shows mild influence on the two-dimensional electron gas channel. In addition, the AlGaN/GaN ISFETs present good pinch-off characteristics in three kinds of solutions with different pH values, showing a sensitivity of approximately 55.5 mV/pH. However, threshold voltage shifting as well as the output current decreasing were observed after worked in alkaline solution. The surface analysis results confirm that the surface was electrochemical etched into many voids, resulting in a positive shift on the threshold voltage. This etching process is related to the surface oxide and dislocation on the high Al-content AlGaN barrier layer. Therefore, the degradation in electrical performances can be attributed to the transformation of AlGaN into surface oxide as well as the followed dissolution in alkaline solution.